A case-control epidemiological study is being undertaken to try to ascertain whether there are any associations, either positive or negative, between use of exogenous estrogenic hormones for therapy during or following menopause or for oral contraception during the reproductive years, and cancer of the corpus uteri, cancer of the breast, and cancer of the ovary. Previous estrogen use in women in the age group 45-74 years admitted to several large Connecticut hospitals with a first diagnosis of any of these cancers will be compared to estrogen use in women in the same age group admitted to the surgical services of the same hospitals for other conditions. Information on estrogen use and other relevant variables is obtained by means of a standardized structured questionnaire administered by trained interviewers; this will be supplemented by information provided by the patient's physician when necessary. Particular attention will be paid to histological type and stage of the disease.